Optimal engineering of CdS/PbS co-sensitized TiO2 nanotube arrays for enhanced photoelectrochemical performance

TiO₂ nanotube arrays (NTAs) are decorated with CdS/PbS nano-sensitizers by successive ionic layer adsorption and reaction (SILAR) method. The uniform growth of the CdS and PbS nanoparticles on the surface and inner side of TiO₂ Nanotube Arrays (NTAs) has been confirmed by Transmission Electron microscopy measurements. The impact of the CdS and PbS semiconductor quantum dots (SQDs) on the photoelectrochemical performance (PEC) of TiO₂ NTAs was systematically investigated, and the optimal decoration of the CdS and PbS SQDs on the TiO₂ NTAs was obtained. CdS/PbS co-sensitized TiO₂ NTA photoanode films show excellent response to visible light (with absorption extended to 825 nm) and enhanced PEC performance. The best performing device showed an enhanced photocurrent density under the 0.62V vs SCE up to 8.2 mA/cm², and high photoconversion efficiency up to 5.35%, which is 16.7 times higher than the pure TiO₂ NTAs. The enhanced PEC performance of TiO₂ NTAs is attributed to the co-sensitization, heterojunction formation and electron “pool” effect imparted on the NTAs by the coupling of CdS and PbS SQDs.     

Visible-light-induced photoelectrochemical behaviors of Fe-modified TiO2 nanotube arrays

Fe-modified TiO(2) nanotube arrays (TiO(2) NTs) were prepared by annealing amorphous TiO(2) NTs whose surface was covered with Fe(3+) by a dip-coating procedure, and characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV-visible reflectance spectroscopy. The photoelectrochemical properties were evaluated by the photocurrent response and photoelectrocatalytic (PEC) degradation of methylene orange (MO) and 4-chlorophenol in water under visible-light irradiation (λ > 420 nm). The results showed that a Fe-modified TiO(2) NTs electrode exhibited a larger photocurrent response and higher PEC activity for the degradation of organic pollutants than a pure TiO(2) NTs electrode. At a bias potential of 0.4 V, the photocurrent response of a 0.5 M Fe-modified TiO(2) NTs electrode exceeded that of a pure TiO(2) NTs electrode by a factor of about 10, and the PEC degradation rates of MO and 4-chlorophenol on a 0.5 M Fe-modified TiO(2) NTs electrode exceeded those on a pure TiO(2) NTs electrode by a factor of about 2.5. The larger photocurrent response and higher PEC activity of Fe-modified TiO(2) NTs could be attributed to the enhancement of separation of charge-carriers at the external electric field and the extension of the light response range of TiO(2) to the visible-light region with the narrowing of the band gap.     

CdSe纳米颗粒敏化TiO_2纳米管阵列的光催化降解及光电催化制氢

采用胶体化学法制备不同尺寸的硒化镉纳米颗粒(CdSe-NP)胶体,并利用原位吸附法将CdSe-NP与由阳极氧化法得到的TiO2纳米管阵列(TN)复合,在可见光下降解甲基橙溶液和外加偏压制氢,分别考察CdSe-NP敏化的TiO2纳米管阵列(CdSe-NP/TN)的光催化性能和光电催化性能。对比TN,CdSe-NP/TN表现出明显增强的光催化活性及更优异的光电催化性能,而过大的CdSe-NP尺寸则不利于复合材料的催化活性。表征结果表明,CdSe-NP/TN优异的性能是由于敏化CdSe-NP后吸收边红移以及光生电子和空穴复合率降低。     

Graphene oxide modified TiO2 nanotube arrays: enhanced visible light photoelectrochemical properties

Novel nanocomposite films, based on graphene oxide (GO) and TiO(2) nanotube arrays, were synthesized by assembling GO on the surface of self-organized TiO(2) nanotube arrays through a simple impregnation method. The composite films were characterized with field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. The photoelectrochemical properties of the composite nanotube arrays were investigated under visible light illumination. Remarkably enhanced visible light photoelectrochemical response was observed for the GO decorated TiO(2) nanotube composite electrode compared with pristine TiO(2) nanotube arrays. The sensitizing effect of GO on the photoelectrochemical response of the TiO(2) nanotube arrays was demonstrated and about 15 times enhanced maximum photoconversion efficiency was obtained with the presence of GO. An enhanced photocatalytic activity of the TiO(2) nanotube arrays towards the degradation of methyl blue was also demonstrated after modification with GO. The results presented here demonstrate GO to be efficient for the improved utilization of visible light for TiO(2) nanotube arrays.     

CdSe敏化TiO2纳米晶多孔膜电极的制备及其光电性能研究

研究了CdSe敏化TiO2纳米晶多孔薄膜电极的制备及其表征,采用涂敷法将溶胶-凝胶法制备的TiO2胶体制备成纳米晶多孔薄膜,采用化学沉积法制备的CdSe对其进行了敏化处理.敏化后增加了对可见光的吸收作用和光生载流子的输运速度,减少了CdSe上光生载流子的复合,改善了电极内光生电荷的传递特性,获得了较大的稳态光电流.这种薄膜电极改进后可用于制作敏化太阳能电池的光阳极.     

氧化钛纳米管阵列制备及应用

氧化钛纳米管阵列因其独特的高度有序的阵列结构而具有良好的力学、化学稳定性以及抗腐蚀性能,在光解水制氢、太阳能电池、光催化、环境净化、气敏传感器等领域具有潜在的应用价值,引起了人们的广泛关注。对近年来TiO2纳米管在制备技术、形成机理、离子掺杂及其应用研究方面取得的成果做了综合评述,在此基础上探讨了TiO2纳米管制备及改性方面存在的问题,并对今后的发展方向予以展望。     

TiO2纳米管阵列粗糙度调控及其与蛋白相互作用

采用电化学阳极氧化法,通过改变电解液氟离子浓度(0.4%、0.3%、0.2%(质量))和电压(15、25、35、45 V),制备一系列不同管径和粗糙度的TiO₂纳米管阵列(TiO₂ nanotube arrays, TNAs)。通过扫描电子显微镜以及原子力显微镜(atomic force microscopy, AFM)表征,结果表明随着电解液中氟离子浓度的降低,制备得到的TNAs表面平整度更好,壁厚增大,粗糙度降低。采用AFM力学表征研究了表面粗糙度以及管径对TNAs表面力学性质以及与细胞色素C(Cytochrome C, Cyt C)相互作用的影响,结果表明,黏附力与接触面积呈正比,随着TNAs管径增加,壁厚减小,TNAs与Cyt C的有效接触面积先增大后减小,两者之间作用力也先增加后减小;同时,同管径条件下粗糙度降低,TNAs有效面积增加,相互作用力也增加;由此可见,通过改变电解液氟离子浓度可以有效调控TNAs表面粗糙度及有效接触面积,进一步利于促进与蛋白分子之间相互作用。     

Synthesis and growth mechanism of multilayer TiO2 nanotube arrays

High-aspect-ratio TiO(2) nanotube arrays formed by anodic oxidation have drawn extensive attention due to their easy fabrication and various excellent optical, electrical and biomedical properties. In contrast to conventional single-layer TiO(2) nanotubes prepared via constant-voltage anodization, we synthesize multilayer TiO(2) nanotube arrays with high surface area by using alternating-voltage anodization steps. This work presents synthesis and growth mechanisms of single-layer smooth TiO(2) nanotubes, bamboo-type nanotubes and double-layer nanotubes, by tuning various parameters such as voltage, time, and water content in the electrolyte. It is found that ion diffusion inside the nanotubes dominates growth of these three structures. A stable pH and ion-diffusion profile allows the steady growth of smooth TiO(2) tubes in NH(4)F-containing ethylene glycol (EG). The addition of a low-voltage anodization step reduces the pH and ion-diffusion gradient in the nanotubes and induces formation of bamboo-type nanotubes and double-layer nanotubes when a second high-voltage anodization is conducted. Ion diffusion through a nanotube takes time; thus formation of lower-layer TO(2) nanotubes costs more time if longer nanotubes are grown in the upper layer, since ions diffuse through these longer nanotubes. This ion-diffusion controlled growth mechanism is further confirmed by tailoring the water content (0-20 vol%) in the electrolyte and the voltage gaps to control the time needed for initiation of lower-layer TiO(2) nanotube arrays. The fundamental understanding of the growth characteristics of double-layer TiO(2) nanotubes presented in this paper offers us more flexibility in engineering morphology, tuning dimensions and phase compositions of multilayer TiO(2) nanotubes. In addition, we synthesize double-layer TiO(2) nanotube arrays composed of one layer of anatase phase and another layer of amorphous phase.     

MoS2 co-catalyst sensitized 3D TiO2/CdS photoanodes with enhanced photoelectrochemical performances

Regulating morphology and constructing heterojunctions to enhance the light absorption and boost the separation of electrons and holes are common and effective means to boost the photoelectrochemical (PEC) performances of TiO₂ photoanodes. In this study, TiO₂ nanoflowers (NFs)/CdS quantum dots (QDs)/MoS₂ nanosheets (NSs) hybrids with two type II band alignments were synthesized by facile hydrothermal, successive ionic layer adsorption and reaction, and dipping methods, respectively. The effects of different amount of MoS₂ co-catalysts on CdS decorated TiO₂ photoanodes were investigated. TiO₂ NFs/CdS QDs/MoS₂ NSs hybrids showed dramatically enhanced PEC performance, especially under visible light illumination. The photocurrent density of TiO₂ NFs/CdS QDs/MoS₂-50 was more than 10 times higher than that of TiO₂ NFs/CdS QDs. This innovative work sheds light on efficiently improving the light absorption by forming heterojunctions and accelerating the electron and hole transfer via specific band engineering design.     

Photoelectrochemical properties of Fe-doped TiO2 nanotube arrays fabricated by anodization

Ti–Fe alloys with Fe contents of 0.05, 0.5 and 1.0 wt% were obtained using the arc-melting method. Fe-doped TiO₂ nanotube arrays were prepared by anodizing Ti–Fe alloys in ethylene glycol solution containing 0.25 wt% NH₄F and 10 wt% H₂O. The microstructure, crystal structure and photoelectrochemical properties of the nanotube arrays were characterized using scanning electron microscopy, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy and electrochemical analyzer. Results show that doping of 0.05 wt% Fe improves the photoelectrochemical properties of titania nanotube arrays significantly, whilst further increasing the Fe contents to 0.5 and 1.0 wt% degrades these properties. The external potential has a considerable influence on the photocurrent density at doping content of 0.5 wt% Fe.     

Efficient PbS/CdS co-sensitized solar cells based on TiO2 nanorod arrays

Narrow bandgap PbS nanoparticles, which may expand the light absorption range to the near-infrared region, were deposited on TiO₂ nanorod arrays by successive ionic layer adsorption and reaction method to make a photoanode for quantum dot-sensitized solar cells (QDSCs). The thicknesses of PbS nanoparticles were optimized to enhance the photovoltaic performance of PbS QDSCs. A uniform CdS layer was directly coated on previously grown PbS-TiO₂ photoanode to protect the PbS from the chemical attack of polysulfide electrolytes. A remarkable short-circuit photocurrent density (approximately 10.4 mA/cm²) for PbS/CdS co-sensitized solar cell was recorded while the photocurrent density of only PbS-sensitized solar cells was lower than 3 mA/cm². The power conversion efficiency of the PbS/CdS co-sensitized solar cell reached 1.3%, which was beyond the arithmetic addition of the efficiencies of single constituents (PbS and CdS). These results indicate that the synergistic combination of PbS with CdS may provide a stable and effective sensitizer for practical solar cell applications.     

Preparation and photoelectrochemical properties of CdS quantum dot-sensitized ZnO nanotube arrays

CdS/ZnO nanotubes (NTs) arrays were synthesized on a transparent conductive glass (FTO) substrate by hydrothermal method, chemical bath etching and successive ionic layer adsorption and reaction (SILAR) method, which were used in semiconductor-sensitized photoelectrochemical cells (PECs). The crystal structure, morphology and photoelectrochemical conversion properties of different photoanodes were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), and electrochemical workstation. The results show a heterojunction has been formed between ZnO and CdS QDs. The ZnO NTs and CdS QDs played a remarkable controllability for PEC performances. The photoelectrochemical conversion efficiency of ZnO NTs photoanodes was 3 times that of ZnO nanorods (NRs) arrays photoanodes. After sensitization of CdS quantum dots, the photoelectrochemical conversion efficiency of CdS/ZnO NRs was improved by 7 times and the CdS/ZnO NTs was increased by 4 times. These results demonstrate that the CdS/ZnO core-shell structure can provide a facile and compatible frame for the potential applications in nanotube-based solar cells.     

High-efficiency dye-sensitized solar cells based on robust and both-end-open TiO2 nanotube membranes

In the present work, dye-sensitized solar cells (DSSCs) were fabricated by incorporating transparent electrodes of ordered free-standing TiO₂ nanotube (TNT) arrays with both ends open transferred onto fluorine-doped tin oxide (FTO) conductive glass. The high-quality TiO₂ membranes used here were obtained by a self-detaching technique, with the superiorities of facile but reliable procedures. Afterwards, these TNT membranes can be easily transferred to FTO glass substrates by TiO₂ nanoparticle paste without any crack. Compared with those DSSCs consisting of the bottom-closed membranes or attached to Ti substrate, the carefully assembled and front-side illuminated DSSCs showed an enhanced solar energy conversion efficiency as high as 5.32% of 24-μm-thick TiO₂ nanotube membranes without further treatments. These results reveal that by facilitating high-quality membrane synthesis, this kind of DSSCs assembly with optimized tube configuration can have a fascinating future.     

Preparation and photocatalytic properties of RuO2/TiO2 composite nanotube arrays

RuO₂/TiO₂ composite nanotube arrays were prepared using an anodic oxidation method combined with dipping. The photocatalytic properties of RuO₂/TiO₂ nanotube arrays in methylene blue solution were investigated under visible light irradiation. The results showed that Ru existing in the form of RuO₂ was dispersed uniformly on the surface of TiO₂ nanotubes, and the RuO₂ did not change the crystal structure of TiO₂ nanotubes. The load of RuO₂ on TiO₂ had a little influence on the band-gap energy and the absorption band edge, but could increase the amount of Ti-OH functional groups on the surface of TiO₂ nanotubes. The RuO₂/TiO₂ nanotube arrays with the optimal photocatalytic activity were formed in the ruthenium chloride solution with a concentration of 0.0030 mol/L. The 2 h photocatalytic degradation rate of methylene blue increased from 38% for pure TiO₂ nanotubes to 69% for RuO₂/TiO₂ nanotube arrays. This work demonstrated that RuO₂/TiO₂ nanotube arrays showed an improved photocatalytic property over pure TiO₂ nanotubes due to the fact that RuO₂ could capture the photo-generated holes, which greatly decreased the recombination of the photo-generated electrons and holes, and hence lengthen the lifetime of photo-induced electrons and increased the amount of hydroxyl groups absorbed on the TiO₂ nanotubes surface.     

Structural and photoelectrochemical characterization of TiO2 nanowire/nanotube electrodes by electrochemical etching

TiO₂ nanowire/nanotube electrodes were synthesized by anodization of titanium foils in ethylene glycol solution containing 0.5 wt% NH₄F and 1 wt% water at 60 V for 6 h. The microstructure and morphology of the asprepared electrodes were investigated by XRD and SEM. A possible formation mechanism and oxidation parameters of nanocomposite structure were discussed. The relationship between structural characteristics of TiO₂ nanowire/nanotube electrodes and its photoelectrochemical characterization were evaluated by electrochemical analyzer and photocatalytic degradation of methylene blue (MB) solution. Furthermore, these TiO₂ nanowire/nanotube electrodes promoted the photoelectrochemical characterization due to the larger surface areas, enhanced light harvesting and electron transport rate. The results show that photocurrent density of 1.44mA/cm² and photocatalytic degradation of 95.51% was achieved for TiO₂ nanowire/nanotube electrodes, which were 0.55mA/cm² and 20.52% higher than the TiO₂ nanotube electrodes under a similar condition, respectively.     

The growth and morphology of copper phthalocyanine on TiO2 nanotube arrays

Nanostructured copper phthalocyanine was deposited by thermal vacuum evaporation, spin-coating, immersion, and electrochemical reactions onto titania nanotubes prepared by the anodization of titanium foil so as to attain interdigited heterojunctions between them for improved interfacial contact. The effects of the titania's crystal structure on the deposition were analyzed. A sodium salt derivative of copper phthalocyanine was used to enhance its affinity to the titania. The deposited copper phthalocyanine could be grown and transformed into diverse morphologies such as polyhedrons, nanorods, and nanowires. The factors affecting the morphology of the deposited copper phthalocyanine were analyzed by SEM and crystal structure analysis.     

Fabrication of CeO2@CdS sub-micron rod arrays for enhanced photoelectrochemical performance

Two-component CeO₂@CdS sub-micron rod arrays with enhanced photoelectrochemical properties were fabricated on Ti substrates by electrodeposition. And it is demonstrated that the enhanced photoelectrochemical properties, compared to those of the pristine CeO₂, are attributed to the suitable type-II band alignment of CeO₂@CdS and the favorable absorption properties of CdS shell.     

Water-splitting properties of bi-phased TiO2 nanotube arrays subjected to high-temperature annealing

An extended study was conducted to correlate between morphological, crystalline phase conversion and the photoelectrochemical water-splitting properties of anodic TiO₂ nanotube arrays (TNTs) films annealed at elevated temperatures, starting from 450 °C to 850 °C. A distinct visualization was provided to support the effect of the high temperature annealing up to 850 °C on the photocurrent productivity of the TNTs films, which acted as photoanodes based on the crystalline anatase-rutile composition ratio. To assess the photoelectrochemical productivity for different annealed materials, several electrochemical techniques were utilized namely; electrochemical impedance spectroscopy (EIS), chronoamperometry and potentiodynamic polarization (PP). Results indicated that the crystalline bi-phased (anatase/rutile) TiO₂ nanotube arrays synergistically influenced the photoelectrochemical water splitting. It was found that the annealed TNTs film with bi-phase content composition (66% anatase and 34% rutile) at 650 °C exhibited maximum photoelectrochemical water-splitting properties with a significant applied bias photon-to-current conversion efficiency (ABPE%) of 0.41%. These results describe a promising target for the fabrication of high performance bi-phase crystalline (anatase and rutile) nanoporous TNTs for improving the photoelectrochemical water-splitting efficiency. Incident photon-to-electron conversion efficiency measurements (IPCE%) also showed the superiority of annealed sample at 650 °C (43.4%), which agrees with EIS, PP and ABPE% calculations.     

TiO_2纳米管在不同条件光催化降解的活性研究

本文利用阳极氧化法在纯钛片表面制备了TiO2纳米管阵列膜,解决TiO2光催化剂的涂敷固定问题。采用场发射扫描电镜(FESEM)和XRD对制备TiO2纳米管阵列膜的形貌和晶体结构进行表征。结果发现,所制得的纳米管管径70～80nm,壁厚5～10nm,XRD显示经420℃热处理的TiO2纳米管为锐钛矿晶型,经500℃热处理的TiO2纳米管出现金红石晶型。以10mg·L-1的甲基橙溶液为降解物进行光催化试验,分别研究了溶液的初始pH值、TiO2纳米管阵列膜的晶型、TiO2膜的使用次数对降解率的影响。试验结果表明,当溶液初始pH值为1时,TiO2纳米管阵列的光催化性能最好,同时随着TiO2膜使用次数的增加,其光催化效果有所下降。